The big picture: Fungi play a role in plant function


  • 100,000 species described
    • estimated 1.5 millions species
    • diverse size, morphology and habitats


  • Heterotrophic: eat via absorption
    • parasites, decomposers, mutualists
    • cycle nutrients via decomposition


  • Cell walls made of chitin
    • mushrooms are only a part of the body
    • filaments belowground absorb things


  • Wild reproduction

All Fungi share traits related to nutrition

Fungal body plan: Not-motile


Most hyphae divided into cells by septa


Mycelium: huge surface and volume for absorption


Specialized hypae in many types of fungi



  • Specialized hyphae for feeding on live animals
    • hoops
  • Specialized hyphae that allow them to extract nutrients from plants

Mycorrhizal fungi: sharing with plants




  • ~80-90% of plants have association with fungus
    • fungi grown in/around plant roots
    • share resources
    • one of the most widespread mutualisms


  • 2 main types:
    • Ecto- and Endo- mycorrhizae
    • diverse array of species for each


  • Association now key for plants to thrive
    • fungi more efficient @ nutrient uptake




  • Branching hyphae used to exchange nutrients with plant hosts


  • Ectomycorrhizal fungi sheath cell walls
    • Hartig net surrounds epidermal cells


  • Endomycorrhizal fungi invade cell walls
    • Arbuscules: highly branched hypae inside cells
    • often called ‘arbuscular’ mycorrhizae

Nutrient Exchange: Sharing is caring





  • Inorganic nutrients imported to plant
    • N, P and amino acids


  • Carbon imported to fungus
    • sugars from photosynthesis


  • Possibly active & passive transport

Soil Life: Plant Roots, Fungi & Microbes



  • Free-living microbial communities in soils breakdown organic matter
    • plants cannot uptake organic compounds
    • fungi lost breakdown enzymes via evolution


  • Microbial communities are carbon limited
    • plants exude carbon (simple sugars) from root tips
    • exudates increases microbial activity


  • Fungi are great at uptake and transport
    • decomposers of some things
    • carbon limited

Timing matters: Land plant evolution & fungi



  • Fungal phyla associated with MS diverged prior to the divergence of land plants
    • Oldest fungal fossils appear ~900 mya
    • First terrestrial fungus ~ 460 mya


  • What was the land like for first plants?
  • What were early plants like?


  • Plant land colonization likely facilitated by interactions with symbiotic fungi
    • fossil evidence shows similarity in timing
    • needs of both groups still relevant

Early lineage plant experiments with fungi: byrophytes


Humphreys et al. 2010

Timing matters: Fossil forests and fungi



  • Vascular plants evolved secondary growth (wood), with lots of lignin
    • lignin is hard to break down


  • About 100 million years of trees sinking into swamps and not decaying
    • carboniferous period = coal deposits


  • Specialized phyla of fungi evolved as wood decay specialist
    • ~295 mya (aka ‘white rot’ fungus)
    • lignin and cellulose


  • What what the world look like today, without this key cog in the carbon cycle?

The current state of agriculture: Role of fungi


Role of mycorrhizae in agrosystems: Nutrients


  • Crop species are breed to be hyper productive
    • fast growing with high yields


  • Roots will rapidly deplete soil nutrients
    • creates depletion zones around root


  • Mycorrhizae extend the reach of roots for nutrients
    • widening the depletion zone


  • Mycorrhizae can also extract nutrients in forms plants cannot
    • phosphorus from DNA or bound to minerals

Innoculate versus fertilize?

The active components in the inoculum are mycorrhizal fungi propagules in the form of spores and colonized root fragments. When one of these colonizing units touches or comes into very close proximity with living root tissue, they are activated by minute amounts of specialized root exudates and begin the colonization process.

  • Commercial fertilizers (NPK) are water-soluble
    • short term availability
    • leaching occurs (aka washes away)
    • results in heavy fertilizer application
  • There are natural abundances of soil nutrients, just not readily or easily accessable to plants
    • bacteria & fungi can help
  • **Mycorrhizae fungi are sensitive to over-watering, pestiticides & excess nutrients

Role of mycorrhizae in agrosystems: Stress


Role of mycorrhizae in agrosystems: Disease


  • The use of pesticides does not aid in a plant’s natural immune response

  • Colonising the plant’s roots and penetrating the root cells with their branching structures, excluding and protecting the roots from pathogens

  • Mycorrhizal fungi also release several antibiotic substances into their mycorrhizospheres

  • Plant communication through MF allows neighboring plants to upregulated immune or defense resoponses

Tomato experiments


Mycorrhizal pre-inoculation significantly enhanced activities of the four enzymes in the leaves upon pathogen infection (early blight disease, Song et al. 2015)

Role of mycorrhizae in agrosystems: Soil Health


  • Management practices that recognize soil health have potential to improve water conservation, nutrient use efficiency and yields

  • Good soil quality reduces erosion & leaching potential

    • hypae release polysaccrides that bind soil particles
  • Good soil quality improves soil organic matter and biodiversity

    Frequent tillage may reduce mycorrhizal associations, and broad spectrum fungicides are toxic to mycorrhizal fungi. Very high levels of nitrogen or phosphorus fertilizer may reduce inoculation of roots.

Sustainable agricultre with mycorrhizae



  • Plant herbivory signals through funagl network between plants
    • neighbors can turn on chemical defenses
    • fungi help induce these chemical defenses (VOC’s)**


  • Nutrients benefits of symbiosis mean more flowers & nectar
    • increases pollination


  • Soil with fungi is more stablity
    • holds more water
    • stores more carbon


  • Heavy metal uptake reduced in plants with fungi symbiosis

Are fungi always a good thing?


The exceptions are many members of the Cruciferae family (e.g., broccoli, mustard), and the Chenopodiaceae family (e.g. lambsquarters, spinach, beets), which do not form mycorrhizal associations. The level of dependency on mycorrhizae varies greatly among varieties of some crops, including wheat and corn.

Lab experiment:

  1. mycorr innoculation
  2. corn, spinach
  3. clear containers
  4. fertilizer (none, regular, high)